The present invention relates to a multiplex transmission method used in, e.g., a vehicle and, more particularly, to a multiplex transmission method for confirming communication nodes connected to a transmission path at the beginning of multiplex transmission.
In recent vehicles, the number of electronic devices equipped in a vehicle is considerably increased along with the development of electronic control, and this results in an increase in the number of wiring lines for connecting the electronic devices, and a complicated wiring structure. In order to solve these problems, as disclosed in, e.g., Japanese Laid-Open Patent Application No. 61-224534, a multiplex transmission method has been examined, and is beginning to be put into practical applications. In this method, signal transmission operations among a plurality of electronic devices are performed in a multiplex transmission mode, i.e., communication nodes of the plurality of electronic devices are connected to a common transmission path, and signal transmission operations among the communication nodes are performed in the multiplex transmission mode.
As a multiplex transmission system for a vehicle, a system, in which communication nodes of various drive controllers such as an EGI controller, a 4WS controller, an ABS/TRC controller, and the like, are connected, and control information is multiplex-transmitted among these nodes, may be proposed. In this case, the types of drive controllers mounted in vehicles are not always the same, and in multiplex transmission apparatuses for vehicles, the types of connected nodes (connection nodes) are not always the same. For example, the types of drive controllers and connection. nodes are different depending on destination countries for the vehicles, such as the U.S.A, EC, Australia, and the like, and are also different depending on grades or options of vehicles even if the vehicles are delivered for the same destination country.
When multiplex transmission is performed, a multiplex transmission apparatus itself must recognize a node connection state of a transmission path (the types of nodes connected to the transmission path). As a method of recognizing the node connection state, the following method of checking the types of connection nodes by the multiplex transmission apparatus itself at the beginning of multiplex transmission may be proposed.
More specifically, the following method may be proposed. That is, a predetermined communication node stores in advance information indicating all the nodes which may be connected in communication involving all the multiplex transmission apparatuses (all the nodes will be referred to as "overall maximum connection nodes" hereinafter, and information indicating the "overall maximum connection nodes" will be referred to as "overall maximum connection node information" hereinafter). At the same time, a predetermined time period (a time long enough for the "overall maximum connection nodes" to transmit the following connection signals) is set. The predetermined communication node requests other nodes to transmit connection signals indicating connections of these nodes, and confirms connection nodes on the basis of the connection signals received within the predetermined time period after the request.
More specifically, the predetermined communication node confirms connections between itself and the nodes, which transmitted the connection signals. If the predetermined communication node receives connection signals from nodes except for itself of the overall maximum connection nodes within the predetermined time period, it determines at that time without waiting an elapse of the predetermined time period that the overall maximum connection nodes are connected, and ends the confirmation of connection nodes.
In the multiplex transmission, it is often required that confirmation of connection nodes performed at the beginning of multiplex transmission be quickly ended, and a multiplex transmission control state for actually performing multiplex transmission be started quickly.
The above-mentioned confirmation method basically requires a considerably long predetermined time period, which is set to be long enough for all of the overall maximum connection nodes to send back signals. In addition, when it can be confirmed within the predetermined time period that all of the overall maximum connection nodes are connected, the confirmation operation is ended at that time. However, the number of actually connected nodes is often smaller than the number of overall maximum connection nodes, and this method cannot always end confirmation within a short period of time.